July 8, 1897] 



NA TURE 



221 



revised edition has added considerably to its utility. It 

 is, indeed, not likely to have a serious rival until the 

 completion of the index-maps of the Geological Survey ; 

 and these will still be on too large a scale for the 

 purposes of a comprehensive view. On the present map, 

 fourteen miles go to an inch ; and we are glad to see 

 that a scale of kilometres is added. The colouring is 

 clear and bold ; and a number of small-type notes along 

 the coast call attention to local details, as is customary 

 in British maps of an educational character. 



A series of well-chosen longitudinal sections occupies 

 the blank spaces in the surrounding seas. It would be 

 an advantage, in the next edition, to be informed as to 

 the length of each section in miles, since some are 

 naturally of a much more general character than others. 

 In one, moreover, the term " Neocomian" is used, though 



iit does not occur in the Table of Systems which forms 

 the index. In another, owing, probably, to the small 

 f scale, there is a striking unconformity between the 

 London Clay and the Bagshot Beds of the London basin. 

 Teachers will be glad to have the Erriboll section, as an 

 example of the northern thrust-planes ; and the whole 

 series will prove of constant service. 



In the index, we note with pleasure the use of " Stones- 

 field Flag" — an "s" is probably omitted — for the well- 

 known but misleading " Stonesfield Slate." In the Pre- 

 cambrian group, the Caledonian Schists, the Hebridean, 

 and the Dalradian, are separately coloured ; and it is 

 tt here that the map is in course of time likely to undergo 

 ^ modification. It has had the advantage of following 

 Sir A. Geikie's recent edition of his map of Scotland, 

 and is naturally a great improvement on other available 

 wall-maps, in which all the schists east of the Torridonian 

 border are classed and coloured as Ordovician. Ireland 

 receives similar treatment ; but here again some re- 

 minder is required of the prudent and cautious language 

 with which the term " Dalradian " was introduced to 

 geologists by its author. The Ordovician areas of 

 eastern Ireland are also likely to become broken up, 

 through the discovery, now announced, of several Silurian 

 districts in their midst. 



In South Wales we have a doubtful boundary, a dotted 

 line, drawn between Silurian and Ordovician ; and in 

 iiiany other of the older areas the map draws attention 

 to recent observations. Even the Lenham Beds receive 

 proper recognition along the scarp of the North Downs. 

 In trying to separate the Old Red Sandstone of 

 southern Ireland into an upper and a lower division, 

 Mr. Johnstone has naturally fallen into the common 

 pitfall. As a matter of fact, the Dingle promontory and 

 the region south of Omagh are the only safe areas where 

 the Lower Old Red Sandstone can be marked out. Prof. 

 Hull drew a provisional line across the centre of the 

 county of Cork, which Mr. Johnstone properly puts aside, 

 as being merely a suggestion. But he carries his Lower 

 Old Red Sandstone along the south of the Blackwater, 

 and colours the same rocks, where they emerge on the 

 north side of the synclinal, as Upper Old Red Sandstone. 

 The logical thing seems to be to use one tint at present 

 for the main Irish Old Red Sandstone, and to split it 

 into two minor tints for the benefit of the Dingle and 

 Tyrone areas. 

 A few misprints require revision in the notes along the 

 NO. 1445, VOL. 56] 



coast, such as " roches monton^es," " Permiam," and 

 "Greenstones" for the town Greystones. There are 

 two references to Eocene plant-beds at Portree, but none 

 at Ardtun, although the unimportant tachylyte at the 

 latter point is mentioned. When we find, however, 

 Radiolarian cherts and the Dover coal among the recent 

 additions to our information on the map, we are not 

 inclined to point out small omissions. We may rather 

 end, as we began, by recommending schools, teachers, 

 and public institutions to place this clear and con- 

 scientious work, without delay, by the side of any older 

 general map which they may happen at present to 

 depend on. 



The earlier edition of Sir A. Geikie's map was ac- 

 companied by a concise handbook dealing with the 

 geological structure of the British Isles. Some such 

 book is obviously desirable, and the new map has 

 provided an excellent opportunity. The progress of Our 

 views regarding the relations of certain strata could have 

 been pointed out, and the meaning of such terms as 

 " Dalradian," " Ordovician," &c., could have been made 

 clear. There was ample room for a picturesque and yet 

 accurate description of the features recorded in the map 

 itself, prominence being given to those aspects of the 

 country that would strike the ordinary traveller. 



In what sense, however, Mr. Johnstone's tabular 

 treatment of elementary mineralogy "accompanies" the 

 map of the British Isles is indeed hard to discover. The 

 author has given excellent and judicious prominence to 

 the localities in which the several minerals occur in the 

 British Isles ; and a series of plates of British fossils 

 occurs as an appendix, repeated, if we mistake not, from 

 the borders of the original map. The revision of the 

 names on these plates still remains to be done ; we have 

 " Fenestalla," " Rhynconella " more than once, "in- 

 crasata," " Cyrene," and divers similar slips. One 

 Eocene mammal is even labelled " Pateo magnum." 

 Our old friend, the seated Pterodactyl, still appears with 

 his five digits on the hand. However, it may be justly 

 urged that these illustrations have nothing to do with the 

 book under review, which is an introduction to the 

 study of minerals. .\s a book of reference for well- 

 taught students, it may have its value ; and we suspect 

 that it has been compiled from notes already found 

 useful by the author in his own courses of instruction. 

 But it suffers from somewhat imperfect proof-reading, as 

 in the case of the formulas of the felspars on page 7 ; the 

 mica formula; also surely require revision. Where, more- 

 over, are "Pary's Mine," " Magee Island," " Penmaen 

 Maur," " Corinthia," and a few others ? 



We confess to feeling afraid of a small work so full of 

 facts and figures ; but its compilation must have involved 

 serious work. The subject is plunged into abruptly, 

 as when we are told in a foot-note on page 1 1 that " a 

 growing together of two or more crystals constitutes a 

 made or twin." It is satisfactory to find a fuller treat- 

 ment of twin-crystals on page 45 ; but the beginner is 

 then informed that "when chemically and physically 

 similar crystals at an early phase of their existence unite 

 at inversely dissimilar parts to form a compound 

 crystalline body, the product is called a twin made, 

 or hemitrope. . . . The plane of junction {plane of com- 

 position) is throughout the tivinning plane in young 



